In high-side semiconductor switches information about the switching state of the high-side switch is often needed to take opportune actions. This information is usually given by a zero-crossing detector which usually is a comparator comparing the potential of a switching node, the source of a MOS transistor, for example, to a reference potential, thus detecting a rising or a falling edge of the switching node.
To give an example, the information when the switching node has actually changed its potential from a low level to a high level may be used for controlling the gate-voltage of a MOS high-side switch in order to reduce conducted electromagnetic emission thus improving electromagnetic compatibility (EMC).
The high-side switch is usually controlled by a floating logic and driver circuit which is supplied by a floating power supply, whereas the zero-crossing detector is usually supplied by a ground related supply voltage. Since the voltages to be switched by the high-side switch can be rather high for an ordinary (CMOS) comparator, the inputs of the comparator have to be especially designed for high voltages. Furthermore, the output of the zero-crossing detector also provides a ground related signal as its output signal which has to be level shifted by an extra level shifter, before it can be further processed by the floating logic controlling the actual switching state of the high-side switch. The additional level shifter has adverse effects on the processing speed of the output signal of the zero-crossing detector, i.e., the output signal is delayed by the level shifter before it can be further processed by the high-side logic.
For an optimal switching operation it is necessary, to detect zero-crossings (i.e., a rising edge) of the signal provided by the switching node as fast as possible.
There is a general need to provide a circuit arrangement comprising a high-side semiconductor switch, a floating driver circuit, and a floating control logic which is able to detect zero-crossings in the signal provided by the switching node very fast and which allows to eliminate the need for a high voltage comparator.